1. Field of the Invention
The present invention relates to a technique for applying space-time block coding (STBC) in consideration of the number of symbols within a slot in a wireless communication system, and a signal transmission method using the same.
2. Discussion of the Related Art
A peak-to-average power ratio (PAPR) is associated with a dynamic range which should be supported by a power amplifier in a transmitting side. A cubic metric (CM) is another value which can express a value indicated by PAPR.
Generally, a single carrier signal exhibits better performance than a multi-carrier signal in CM or PAPR. A 3rd generation partnership project (3GPP) long-term evolution (LTE) system uses single carrier frequency division multiple access (SC-FDMA) so that uplink transmission from a user equipment (UE) to a Node B (or eNB) may have a single carrier characteristic due to PAPR/CM problems. In a 3GPP long term evolution-advanced (LTE-A) system, a multiple input multiple output (MIMO) transmission scheme using the SC-FDMA has been discussed to maintain a good CM characteristic.
Hereinafter, the MIMO transmission scheme will be described in brief.
MIMO refers to a method capable of improving transmission/reception data efficiency using multiple transmit antennas and multiple receive antennas, instead of a conventional method employing one transmit antenna and one receive antenna. That is, MIMO is an application of technology that gathers fragmentary data pieces received from multiple antennas into one and constructs data, without depending upon a single antenna path to receive one whole message. The MIMO technology can improve a data transmission rate within a specific range or can increase a system range with respect to a specific data transmission rate. The MIMO technology is a next-generation mobile communication technology which can be widely used in mobile communication terminals, repeaters, etc.
FIG. 1 illustrates the construction of a general MIMO system.
If the number of antennas is simultaneously increased in both a transmitting side and a receiving side, since theoretical channel transmission capacity is increased in proportion to the number of antennas, unlike the case in which multiple antennas are used in either the transmitting side or the receiving side, frequency efficiency can be remarkably improved.
In a trend in research up to now related to multiple antenna technologies, active studies have been conducted in many aspects, including research into information theory related to the capacity computation of multiple antenna communication in various channel environments and in multiple access environments, research into wireless channel measurement and introduction of MIMO systems, and research into space-time signal processing technologies for improving transmission reliability and a transmission rate.
MIMO technology includes a ‘spatial diversity’ scheme for increasing transmission reliability using symbols passing through various channel paths and a ‘spatial multiplexing’ scheme for improving a transmission rate by simultaneously transmitting a plurality of data symbols using a plurality of transmit antennas. Recently, studies on a method of combining the above-described schemes to take advantage of the respective schemes have been carried out.
A description of the aforementioned schemes will now be given in detail.
First, the spatial diversity scheme includes a space-time block coding method, and a space-time trellis coding method using both a diversity gain and a coding gain. The trellis coding is generally excellent in terms of improvement of a bit error rate and the degree of freedom in generating codes but the space-time block coding method is simple in terms of computation. The space diversity gain can be obtained from a multiplication of the number of transmit antennas and the number of receive antennas. Meanwhile, a ‘space-time coding method’ may be regarded as a ‘space-frequency coding method’ when considering a frequency region instead of time and the same coding scheme is applied to both cases.
Second, the spatial multiplexing scheme transmits different data sequences through respective transmit antennas. At this time, in a receiver, mutual interference may be generated between data which is simultaneously transmitted from a transmitter. Then the receiver eliminates the interference using proper signal processing methods and receives the data. The receiver used for eliminating the interference includes a maximum likelihood receiver, a zero forcing (ZF) receiver, a minimum mean square error (MMSE) receiver, a diagonal Bell laboratories layered space-time (D-BLAST) receiver, and a vertical Bell laboratories layered space-time (V-BLAST) receiver. Especially, if the transmitter is aware of channel information, a singular value decomposition (SVD) method may be used to eliminate the interference.
Third, a combination of the spatial diversity scheme and the spatial multiplexing scheme may be used. If only the spatial diversity gain is obtained, a gain in performance improvement caused by an increase in a diversity order is gradually saturated. If only the spatial multiplexing gain is obtained, the transmission reliability of a wireless channel is decreased. Accordingly, studies into a method for solving theses shortcomings and simultaneously obtaining the spatial diversity gain and the spatial multiplexing gain have been conducted. As a result, double space-time transmit diversity (double-STTD), and space-time bit interleaved coded modulation (STBICM) have been used.
In the above-described MIMO system, transmission efficiency may be increased by multiplying a weight to a transmission signal through each antenna. Multiplexing a weight to a transmission signal is called precoding.
When using general precoding, since information signals corresponding to multiple layers are multiplexed and transmitted in terms of one antenna, a transmission signal may be regarded as a kind of a multicarrier signal. Namely, deterioration of CM characteristics of the transmission signal may occur through precoding.
When considering the reason why the CM characteristics are lowered by precoding, if multiple single carrier signals having good CM characteristics are simultaneously overlapped, it may be appreciated that the CM characteristics are deteriorated. Therefore, if information generated from multiple layers in an SC-FDMA system is mapped to single carrier signals of a number as small as possible and multiplexed and transmitted through one physical antenna, good CM may be maintained.
Meanwhile, in a transmit diversity technique of the above MIMO scheme, special processing is performed with respect to information during transmission. Accordingly, a receiving side may ensure reliability to some degree through the transmit diversity even though a part of a channel is in a bad environment. The transmit diversity is generally used when a UE is at a cell edge and may be used in environments in which channel-dependent scheduling is difficult due to rapid variation of a channel or a channel is abruptly varied. In addition, there are various environments and conditions in which the transmit diversity scheme can be used.